I should stop there, but I will say that no one can predict quakes in any useful way.
California's biggest quakes will be in the range of 7.8-8.0, quite a few times smaller than an 8.4. The stresses are there for a large quake to happen, but a magnitude 8 quake is given only a 4% chance of occurring sometime in the next 30 years.
Please don't believe everything that tweets....
But do prepare for quakes in California. They CAN happen any time, but NO ONE can predict them.